Multiple propellent grain for rocket motors



Nov. 16, 1965 J. v. BRAUN ETAL MULTIPLE PROPELLENT GRAIN FOR ROCKETMOTORS 3 Sheets-Sheet 1 Original Filed Oct. 51, 1960 INVENTORS. WILLARD5. BACON JANE-3 V- RflU/V BY ATTORNEYS Nov. 16, 1965 J. v. BRAUN ETALMULTIPLE PROPELLENT GRAIN FOR ROCKET MOTORS Original Filed Oct. 51, 19603 Sheets-Sheet 2 WAAg INVENTORS. WILLARD .3 BACON BY JAM$ v. BRflU/vATTORNEYS Nov. 16, 1965 J, v. BRAUN ETAL MULTIPLE PROPELLENT GRAIN FORROCKET MOTORS Original Filed 001;. 31, 1960 5 Sheets-Sheet 3 V vv\\\\\wwINVENTORS. W/LLHRD S. BACON JAMES v B/a/w/v LLJ ATTORNEYS United StatesPatent 3,217,651 MULTIPLE PROPELLENT GRAIN FOR ROCKET MOTORS James V.Braun, Lewisburg, Ohio, and Willard S. Bacon,

Columbia, Mo., assignors to the United States of Amerlea as representedby the Secretary of the Air Force Original application Oct. 31, 1960,Ser. No. 66,360, now

Patent No. 3,165,060, dated .Jan. 12, 1965. Divided and this applicationNov. 13, 1963, Ser. N 0. 323,510

36 Claims. (Cl. 102-98) (Granted under Title 35, U.S. Code '(1952), see.266) The invention that is described herein may be manufactured and usedby or for the Government for governmental purposes without, the paymentto us of any royalty thereon.

This is a divisional application of our application Multiple PropellentGrain for Rocket Motors, Serial No. 66,360, filed October 31, 1960, andissued on January 12, 1965, as US. Patent No. 3,165,060.

This invention relates to solid propellants for rocket motors and moreparticularly to the structure of grains that each contains a pluralityof propellants.

As a background for imparting a clear understanding of the presentinvention as claimed are cited the George P. Sutton book RocketPropulsion Elements, published in 1956 by John Wiley and Sons, Inc., NewYork city, New York; Principles of Polymer Chemistry by Paul J. Flory,published in 1953 by the Cornell University Press, Ithaca, New York; TheBritish Interpl-anetary Society Journal, volume 16, No. 17 dated Octoberto December 1957 at pages 198 to 211, inclusive; Jet Propulsion ofFebruary 1956 at pages 102 to 105; US. Letters Patents No. 2,661,692 toVegren; No. 2,820,410 to Tarr; No. 2,703,960 to Prentiss; No. 2,681,619to Chandler; No. 2,524,591 to Chandler; and No. 1,074,809 to Newton.

Previously available perforated grain solid propellants do not permitthe most eificient use of the available volume within the case becausepart of the case contains no propellant.

An object of this invention is to completely fill the case or shell witha plurality of solid propellants to provide a grain of materiallysuperior performance as compared with any grain available previously.This invention provides a multiple propellent grain that comprisespropellants of diiferent burning rates and that permits the use of veryhigh burning rate propellants, the previous use of which has beendifficult or impossible.

Another object is to provide solid propellent grains that consist ofmultiple propellants of predetermined mathematically and geometricallyprecise symmetrical forms, shaped as cones, cylinders, cups, etc., thatare dimensioned, positioned and proportioned such that they burnsimultaneously and are simultaneously completely consumed and therebycontinuously, steadily and smoothly deliver their optimum thrust fromthe time of their ignition to the time of their burnout. In thisconnection, attention is invited to FIGS. 5 and 7 on pages 205 and 207of the British Journal article.

The present invention has as its nature and substance the provision of agenerally cylindrically shaped rocket motor charge having a fiat,circular base at one end and a se-mispherical portion at the end remotefrom the flat, circular base and that is composed of a plurality ofpropellants of prescribed and graduated burning rates, advantageouscontours and dimensions such that the burning of all of the propellantsin a grain ends at the same time. This result is accomplished bydesigning the propellants as long cone structures with sharp edges andpoints and with mathematically determined inclinations and proportionatedimensions that collectively provide a materially improved volumetricburning efficiency high mass ratio, low center of gravity travel andthat eliminates "ice previously encountered ditficulties in burninghigh-burning rate propellants.

Illustrative embodiments of the present invention as embodied in moldedgrains and each grain consisting of multiple propellants are shown inthe accompanying drawings, wherein:

FIG. 1 is an axial sectional view of a two-propellent grain;

FIG. 2 is a plan view from below of the grain that is shown in FIG. 1;

FIG. 3 is an axial sectional view of a two-propellent grain;

FIG. 4 is a plan view from below of the grain that is shown in FIG. 3;

FIG. 5 is an axial sectional view of a two-propellent grain;

FIG. 6 is a plan view from below of the grain that is shown in FIG. 5;

FIG. 7 is an axial sectional view of a three-propellent grain;

FIG. 8 is a plan view from below of the grain that is shown in FIG. 7;

FIG. 9 is an axial sectional view of a three-propellent grain;

FIG. 10 is a plan view from below of the grain that is shown in FIG. 9;

FIG. 11 is an axial sectional view of a three-propellant grain; and

FIG. 12 is a plan view from below of the grain that is shown in FIG. 11.

The propellent grains that are illustrated in the accompanying drawingsare illustrative of operative grains that fit into a hollow rocket case,not shown, that is cylindrical and that is open at one end. The casecommonly comprises a wall of 41-30 steel, of the composition with ironof C 0.28 to 0.33; Si 0.20 to 0.35; P 0.04 maximum; Cr 0.80 to 1.10; Mn0.40 to 0.60; and others 0.15 to 0.25.

The illustrative operative grains are 14.5 cm. long and 5.0 cm. indiameter. The operative grains consist of a plurality of propellantsthat completely fill the rocket case and cover its inner surface priorto burnout. The plurality of propellants in each grain are end-burningand burn simultaneously. The different propellants in each grain aredesigned to start and to stop burning together. This characteristicaifords a uniform and maximum propulsion force continuously delivered byeach grain during its burning period. This result is accomplished by thespatial distribution of the propellants in each grain referred to thebase or flat bottom end of the grain as plane of reference, coupled withthe burning rate of the propellants in the grain.

In FIG. 1 of the accompanying drawings for example, the grain consistsof the fast-burning propellant 1 interleaved with the more slowlyburning propellant 2 or in FIGS. 7 to 12 inclusive, the more slowlyburning propellant 3 depending on the geometry of the grain.

A solid propellant to satisfy the requirements of the grain is made froma liquid polymeric substance and an oxidizer which are intimately mixedand then solidified by chemically curing the polymer. A polymericmaterial which satisfies the requirements of propellant 1 is 11,12dicarbadodecaborane with the empirical formula 2 1u 12)x and of thestructural formula (CCR)X BioHm wherein R is a polymeric coupling moityselected from the group illustratively of vinyl (C C) and carboxyl O(at-0a etc. and x signifies the repetition of the polymeric structure.

The fast-burning propellant is comprised of the above polymeric materialor a satisfactory substitute, and an oxidizer such as ammoniumperchlorate of the formula NH ClO The oxidizer, which is normallycrystalline is finely ground and is mixed with the uncured liquidpolymer at slightly elevated temperatures of from 120 to 150 F. and oneatmosphere of pressure. This liquid mix contains 70 to 85 percent byweight of oxidizer and is of sufficiently low viscosity to permitpouring by gravity around a forming mandrel.

The propellent grain is formed directly into the case in which it is tobe used and is then cured by maintaining the entire mass at elevatedtemperatures of from 120 to 150 F. for a period of 24 to 72 hours forfurther polymerization. Manufacturing details of this grain followstandard practices as outlined in chapter 10, of Rocket PropulsionElements by George P. Sutton.

The slow-burning propellant illustratively is ammonium perchlorate inamounts from 70 to 85 percent by weight mixed with polybutadiene acrylicacid polymer as set forth hereinafter.

The two propellants are to be ignited simultaneously at the base of thegrain inwardly of a restrictor of asphalt, rubber, or the like. Thepropellants are to burn at different but uniform rates and are to ceaseburning at the same time. The geometric aspect of the propellants inFIG. 1 are characteristic of the grains in the other figures of thedrawings.

In FIGS. 1 and 2 the fast-burning 11,12 dicarbadodecaborane propellant 1projects upwardly from the grain base Within the more slowly burningpropellant 2. The propellant 1 is in the shape of an upwardly opening V-shaped cup that terminates at the top in a rim 11. The cup is asymmetrical body of uniform composition and is filled with thepropellant 2. The rim 11 of the cup is closer radially to the rocketcase than is the bottom of the cup and to accomplish this result acollapsing type of mandrel that is common in the trade is used. Thepropellant 2 fills the V-shaped upwardly opening cup with a symmetricalconical portion that terminates downwardly in a cone apex 12. The apex12 of the propellant 2 cone terminates downwardly in the center of thegrain base with sufiicient propellant 2 exposed for being ignited at thebase simultaneously with the lighting of the propellant 1 radiallyinwardly from the restrictor 10.

The circular flat restrictor 10 is made of asphalt, rubber, or the like,and covers the propellant 2 at the grain base, leaving for thesimultaneous ignition of the grain the base of the propellant 1 and theapex 12 of the centrally disposed propellant 2 cone. The cone of thepropellant 2 extends centrally of the grain with the propellant 1positioned between the cone and the outer part of the propellant 2 at anaccurately defined angle on with reference to the base, as indicated tothe left of FIG. 1.

The angle a has a particular value that is determined for a particularpropellant by its characteristics of burning rate 'y, time of burning tand the distance I the propellant extends up into the grain.

In the diagram to the left of FIG. 1, with AB parallel to the generatrixof the grain cylinder and AC parallel to AC' of the propellant 1,

cos a= Z2 With the factor subscripts indicating the first and secondpropellants and the propellant-burning time t equal to thepropellant-burning time t then the values are:

By substituting for particulan propellants the known values of theirburning rates and their lengths, the angle a is determined such that thepropellants are consumed at the same time and no unburned sliver ofpropellant remains in the rocket case.

In FIG. 1 of the accompanying drawings for the grain size shown, theangle a illustratively is about 88, the center cone tip 12 or cone apexangle illustratively is about 17 and the angle at the upper edge 11 ofthe propellant 1 illustratively is about 6.

The multiple propellants that are referred to herein are those that arecurrently used for their value of propulsion in rocketry and are roughlydistinguished from each other herein by their relative burning rates asbeing fast propellant 1, intermediate propellant 2 and slow propellant3. Illustrative burning rates are given on page 202 of the BritishJournal article and in the Sutton reference at pages 312 to 317 and 350.

For both di-propellent grains and for tri-propellent grains that aredisclosed herein, the fast propellant 1 has the same illustrative valueof burning rate range per sec 0nd of from 1 inch to inches. Thetri-propellent intermediate propellant 2 has an illustrative burningrate per second of from 0.2 inch to 1 inch. The tri-propellent slowpropellant 3 has an illustrative burning rate of from 0.05 inch to .2inch. The size and shape of a rocket motor effects the burning rates ofthe propellants that are used in the rocket case of the rocket motor.

The propellants commonly used in rocketry may be divided roughly intothe groups that are referred to above as fast 1, intermediate 2, andslow 3.

Specific high energy system fast-burning rate propellants 1 arerepresented illustratively herein by the compound 11,12dicarbadodecaborane. Other propellants with fast-burning rates are highenergy systems that are commercially available as polymeric compoundssuch as combustible polymers that have high contents of nitrogen,nitrogen and boron, nitrogen and fluorine and the like.

Propellants of the intermediate burning rate 2 illustratively are fullyor highly nitrated cellulose and glycerine compounds, ammoniumperchlorate mixed with other compounds such as selected polymers,powdered aluminum for its exothermic energy content and the like.Commercially available materials in this group are designated in thetrade as high and low burning rate double base nitroglycerine andnitrocellulose which are plastisols, composites of crystalline materialswith polymers, and the like. Particular composite binders arepolyurethane, polybutadieneacrylic acid polymer that is merchandisedunder the title PBAA polysulfide, polyesters, polyacrylates, polyvinylchloride, polyvinyl acetate, butyl rubbers, and the like.

Propellants of the slow-burning rate 3 may be illustrated by compositesusing as an oxidizer ammonium nitrate mixed with, as binder celluloseacetate or polyurethane, equal parts of polybutadiene and acrylic acidcopolymer, polybutadiene methyl vinylpyridine copolymer, a polysulfidepolymer of linked hydrocarbons, commercially available rubber such asbutyletherpolysulfide polymer and the like.

FIGS. 3 and 4 illustrate a tWo-propellent grain that comprises afast-burning propellant 1, such as 11,12 dicarbadodecaborane interleavedwith an intermediate burning rate propellant 2, such as ammoniumperchlorate and PBAA or the like. The angle a at the base isillustratively 88, as in FIG. 1. A restrictor 15 of asphalt, rubber, orthe like, covers the outer ring base portion of the propellant 2. Inthis structure the grain is ignited inwardly of the restrictor 15 at thebase 16 of the propellant 1 and the lower ring edge or rim 17 of thepropellant 2. Thepr-opellant 2 lower ring edge or rim 17 measures 8. Thepropellant 1 upwardly opening cup concentric with the cone terminatesupwardly in an edge 18 that measures 3 The propellant 1 upper cone apex19 measures 5.

FIGS. 5 and 6 illustrate a two-propellent grain that comprises afast-burning propellant 1, such as 11, 12 dicarbadodecadorane and anintermediate burning rate propellant 2, such as, ammonium perchloratewith PBAA. The fast-burning propellant 1 is shaped as a pair of coaxialupwardly opening c-ups that contain propellant 2 and with their coaxialring bases 21 and 22 within the plane of the grain base and the cupwalls tapering upwardly to thin inner and outer cup rims that are remotefrom the grain base. The inner cup wall rim is spacially farther awayfrom the grain base than is the outer cup wall rim. Both cup walls havethe slower propellant interposed therebetween as well as outside theouter cup wall. The base of the inner cup is separated from the base ofthe outer cup in the plane of the grain base by a thin section of theslow-burning rate propellant in an edge or rim 24. The angle ,8 made bythe outer side interface of the propellants 1 and 2 with the grain baseis 89. A restrictor of asphalt, rubber, or the like, covers the outsidering base portion of the propellant 2.

In this structure the grain is ignited inwardly of the restrictor 20 atthe more rapidly burning propellant 1 base rings 21 and 22 and the basetips of the more slowly burning propellant 2 central cone apex 23 andthe edge or rim 24. The propellant 2 central cone lower apex 23 measures8. The propellant 2 ring downwardly tapering lower edge 24 measures 4.The propellant 1 inner ring upper edge measures 3 and the outer ringupper edge measures 4.

FIGS. 7 and 8 illustrate a three-propellent grain comprising afast-burning propellant 1 as a central cone of 11,12 dicarbadodecaboranewith its base 25 inwardly from a restrictor 26 of asphalt, rubber, orthe like, and terminating upwardly in an apex 27 that measures 13; anintermediate propellant 2 of ammonium perchlorate with PBAA openingdownwardly as a cup around the cone of propellant 1 and the cup walltapering downwardly to the grain base in a ring edge that measures 11;and a slow propellant 3 of ammonium nitrate mixed with cellulose acetateor the like, outer cylinder with a wall that tapers upwardly to an edge28 that measures 5 and that thickens downwardly to make an inner angle 6of 85 with the base.

FIGS. 9 and 10 illustrate a three-propellant grain that comprises afast-burning propellant 1 with its base 31 in the plane of the grainbase and that is in the form of an upwardly open cup with a side wall ofdiminishing thickness that terminates upwardly in an edge that measures8; an intermediate propellant 2 that consists of a central cone portionthat tapers downwardly to an apex 29 that measures 9 at centrally of thegrain base and downwardly to an open cup portion starting from bothsides of the propellant 1 edge 30 as a downwardly open cup with adownwardly tapering wall that terminates downwardly at the grain base inan edge 32 that measures 6; and a slow propellant 3 that is covered atthe base by the restrictor 33 and that is a cylindrical wall thatbecomes more thin upwardly to an edge 34 that measures 5. The slowpropellant interface with the intermediate propellant makes an angle awith the base of 86.

The central cone portion of the intermediate burning rate propellant 2is generated around an axis that is coaxial with the axis of the overallcylindrically shaped body of the rocket propellant grain, as are all ofthe other conical shapes of the rocket propellants that are disclosedherein. As are shown in all of the drawings, the overall cylindricallyshaped rocket propellant body has a circular, fiat bottom end,cylindrical sides and an upper or top end that is half a sphere.

A restrictor that is made of asphalt or rubber and that is shaped like aflat washer overlies and is glued to the bottom end of the overallcylindrically shaped body of the rocket propellent grain. The restrictoroverlies the slow propellant in the plane of the flat bottom end of theoverall cylindrically shaped rocket propellent grain body.

FIGS. 11 and 12 illustrate a three-propellent grain that comprises afast-burning propellant 1 with a central cone that rises from its base35 to its apex 36, with an apex angle of 6 concentric with a ring thatrises from its base 37 to an upper edge 38 that measures 5; andintermediate-burning rate propellant 2 that tapers downwardly to thebase in concentric inner and outer edges that each measures 5; and aslow-burning rate propellant 3- that at the base is covered by therestrictor 39 and that tapers upwardly to an edge 40 that measures 4.The slow propellant 3 inner angle eta with the base is 86 to the base.

It is to be understood that the contours, dimensions, angles and thepropellent compositions that are disclosed herein may be modifiedsomewhat to accommodate particularly desirable combinations andstructures.

We claim:

1. A generally cylindrical end burning propellent grain having a flatcircular base at one end and a semispherical portion at the other end,said propellent comprising two charges, one of said charges having afast and the other of said charges having a slower-burning rate, a firstconical slower-burning charge positioned along the longitudinal axis ofthe cylindrical propellent grain, the apex of the said conical portionbeing located in the plane of said circular base, the base of theconical portion being integral with the semispherical portion, anannular fastburning charge surrounding and in contact with the conicalslower-burning charge, said fast-burning charge having a base portionlocated in the plane of the said circular base, said annularfast-burning charge having walls narrowly tapering from said base andextending to said semispherical portion, a second-slower burning annularcharge surrounding and in contact with said fastburning charge, saidsecond slower-burning charge having a base portion located in the planeof the said circular base and having a narrowly tapered wall extendingto said semispherical portion.

2. The grain defined by claim 1 wherein the conical slower-burningcharge tapers into an apex of about 17 degrees.

3. The grain defined by claim 1 wherein the interface of the secondslower-burning annular charge with the fast-burning charge forms anangle of about 88 degrees with the grain base.

4. The grain defined by claim 1 wherein the fast-burning charge forms anaxially open cup filled with the slower-burning propellant and has aterminal upper edge of about 6 degrees.

5. The grain defined by claim 1 wherein a restrictor covers the outsidebase portion of the slower-burning propellant.

6. The grain defined by claim 1 wherein the fast-burning charge is thepolymeric material derived from 11,12 dicarbadodecaborane and 70 toweight percent ammonium perchlorate as oxidizer, within the temperaturerange of to degrees F. at about one atmosphere of pressure for from 24to 72 hours and the slower-burning propellant is from 70 to 85 weightpercent ammonium perchlorate polybutadiene acrylic acid polymer.

7. The grain defined by claim 1 wherein the fast-burn ing charge has aburning rate in the range of from 1 to 100 inches per second.

8. A generally cylindrical end burning propellant grain having a fiatcircular base at one end and a semispherical portion at the other end,said propellant comprising two charges, one of said charges having afast and the other of said charges having a slower-burning rate, a firstconical fast-burning charge positioned along the longitudinal axis ofthe cylindrical propellant grain, the base of the conical portion beinglocated in the plane of said circular base, the apex of the conicalportion extending to the semispherical portion, an annularslower-burning charge surrounding and in contact with the conicalfast-burning charge, said slower-buring charge having a base portionintegral with the semispherical portion said annular slower-burningcharge having walls narrowly tapering to said circular base, a secondfast-burning charge surrounding and in contact with the said annularslower-burning propellant charge, the said fast-burning charges having abase portion located in the plane of the said circular base, saidannular fast-burning charge having walls narrowly tapering from saidbase and extending to said semispherical portion, a secondslower-burning annular charge surrounding and in contact with saidsecond fastburning charge, said second slower-burning charge having abase portion located in the plane of the said circular base and having anarrowly tapered wall extending to said semispherical portion.

9. The grain defined by claim 8 wherein the fast-burning conical portiontapers into an apex of about degrees.

10. The grain defined by claim 8 wherein the interface of the secondslower-burning charge with the second fastburning charge makes an angleof about 88 degrees with the grain base.

11. The grain defined by claim 8 wherein the second fast-burning chargeforms an upwardly opening cup and has an edge terminating upwardly in anangle of about 3 degrees.

'12. The grain defined by claim 8 wherein a restrictor covers theoutside base portion of the second slowerburning charge.

13. The grain defined by claim 8 wherein the fastburning charge is apolymeric derivative of 11,12 dicarbadodecaborane and from 70 to 85weight percent ammonium perchlorate cured at one atmosphere pressure forfrom 24 to 72 hours within the temperature range of from 120 to 150degrees F., and the slower-burning charge is from 70 to 85 weightpercent ammonium perchlorate polybutadiene acrylic acid polymer.

14. The grain defined by claim 8 wherein the fastburning charge has aburning rate in the range of from 1 to 100 inches per second.

15. A generally cylindrical end burning propellant grain having a flatcircular base at one end and a semispherical portion at the other end,said propellant comprising two charges, one of said charges having afast and the other of said charges having a slower burning rate, a firstconical slower burning charge positioned along the longitudinal axis ofthe cylindrical propellant grain, the apex of the conical portion beinglocated in the plane of said circular base, the base of the conicalportion being integral with the semispherical portion, a first annularfast-burning charge surrounding and in contact with the said conicalslower burning charge, said fast-burning charge having a base portionlocated in the plane of the said circular base, said annular fastburning charge having walls narrowly tapering from said base andextending to said semispherical portion, a second slower annularpropellant charge extending from said semispherical portion surroundingand in contact with said fast-burning charge, said second slower chargehaving walls narrowly tapering from said semispherical portion andextending to said circular base, a second fast-burning annular chargesurrounding and in contact with said second slower-burning annularcharge, said second fast-burning charge having a base portion located inthe plane of the said circular base and having narrowly tapered wallsextending to said semispherical portion, a third slower-burning annularcharge, said third slower-burning charge having a base portion locatedin the plane of the said circular base and having a narrowly taperedwall extending to said semispherical portion.

16; The grain defined by claim 15 wherein the first annular fast-burningcharge and the second fast-burning annular charge form a pair of coaxialand upwardly opening cups having upper rims which taper to angles ofabout 3 to 4 degrees.

17. The grain defined by claim 15 wherein the first conicalslower-burning charge tapers downward to an apex of about 8 degrees.

18. The grain defined by claim 15 wherein the second slower annularpropellant charge tapers downwardly to an edge of about 4 degrees.

19. The grain defined by claim 15 wherein the interface of the thirdslower-burning charge with the second fast-burning annular charge formsan angle of about 89 degrees with the grain base.

20. The grain defined by claim 15 wherein a restrictor covers theoutside base portion of the third slower-burning charge.

21. The grain defined by claim 15 wherein the fastburning propellentcharge is a combustible derivative of 11, 12 dicarbadodecaborane mixedwith 70 to weight percent ammonium perchlorate and the slower-burningcharge is from 70 to 85 percent ammonium perchlorate in polybutadieneacrylic acid polymer.

22. The grain defined by claim 15 wherein the fastburning charge has afast-burning charge in the range of from 1 to inches per second.

23. A generally cylindrical end burning propellant grain having a fiatcircular base at one end and a semispherical portion at the other end,said propellant comprising three charges, each of said charges having adifferent burning rate, a first conical fast-burning charge positionedalong the longitudinal axis of the cylindrical propellant grain, thebase of the conical portion being located in the plane of said circularbase, the apex of the conical portion extending to the semisphericalportion, an annular intermediate burning charge surrounding and incontact with the conical fast-burning charge, said intermediate chargehaving an annular wall narrowly tapering from said semispherical portionand extending to said circular base, a slow burning annular chargesurrounding and in contact with said intermediate burning charge, saidslow burning charge having a base portion located in the plane of thesaid circular base and having a narrowly tapered wall extending to saidsemispherical portion.

24. The grain defined by claim 23 wherein the fastburning propellanttapers into an apex of about 13 degrees.

25. The grain defined by claim 23 wherein the annular wall of theintermediate burning charge tapers downward 13 to a ring edge of about11 degrees.

26. The grain defined by claim 23 wherein the narrowly tapered wall ofthe slower-burning annular charge tapers upwardly to form an edge ofabout 5 degrees with the outer cylinder wall.

27. The grain defined by claim 23 wherein the interface between theslower-burning annular charge and the intermediate annular charge formsan angle of about 85 degrees with the grain base.

28. The grain defined by claim 23 wherein the fastburning charge is thepolymeric material derived from 11,12 dicarbadodecaborane mixed withfrom 70 to 85 Weight percent ammonium perchlorate as oxidizer cured atone atmosphere pressure for from 24 to 72 hours within the temperaturerange of from to degrees F., the intermediate propellant is highlynitrated cellulose, and the slower propellant is from 70 to 85 weightpercent ammonium nitrate in polybutadiene acrylic acid polymer.

29. The grain defined by claim 23 wherein the fastburning charge has aburning rate in. the range of 1 to 100 inches per second, theintermediate burning charge has a burning rate in the range from 0.2 to1 inch per second, and the slower-burning charge has a burning rate offrom 0.05 to 0.2 inch per second.

30. A generally cylindrical end burning propellant grain having a flatcircular base at one end and a semispherical portion at the other end,said propellant comprising three charges, each of said charges having adifierent burning rate, a first conical fast burning charge positionedalong the longitudinal axis of the cylindrical propellant grain, thebase of the conical portion being located in the plane of said circularbase, the apex of the conical portion extending to the semisphericalportion, an annular intermediate burning charge surrounding and incontact with the conical fast burning charge, said intermediate burningcharge having walls narrowly tapering from said semispherical portionand extending to said circular base, a second fast-burning annularpropellant charge having a base portion located in the plane of the saidcircular base, said annular fast burning charge having walls narrowlytapering from said base and extending to said semispherical portion andin contact with said intermediate burning charge, a second intermediateburning annular charge surrounding said second fast burning charge, saidsecond intermediate burning charge having Walls narrowly tapering fromsaid semispherical portion and extending to said circular base, a slowburning annular charge surround-ing and in contact with said secondintermediate burning charge, said slow burning charge having a baseportion located in the plane of the said circular base and having anarrowly tapered wall extending to said semispherical portion.

31. The grain defined by claim 30 wherein the first conical fast-burningcharge tapers into an apex of about 6 degrees.

32. The grain defined by claim 30 wherein the annular fast,intermediate, and slow-burning charges taper to an edge having an anglein the range of about 4 to 5 degrees.

33. The grain defined by claim 30 wherein the interface between theslower-burning annular charge and the second intermediate-burningannular charge makes an angle of about 86 degrees with the base ofgrain.

34. The grain defined by claim 30 wherein a restrictor covers theoutside base portion of the slower-burning propellant.

35. The grain defined by claim 30 wherein a fast-burning charge is thepolymeric material derived from 11,12 dicarbadodecaborane mixed withfrom to weight percent ammonium perchlorate as oxidizer cured at oneatmosphere pressure for from 24 to 72 hours within the temperature rangeof from to degrees F., the intermediate propellant is highly nitratedcellulose, and the slower propellant is from 70 to 85 weight percentammonium nitrate in polybutadiene acrylic acid polymer.

36. The grain defined by claim 30 wherein the fast-buming charge has aburning rate in the range of 1 to 100 inches per second, theintermediate burning charge has a burning rate in the range from 0.2 to1 inch per second, and the slower-burning charge has a burning rate offrom 0.05 to 0.2 inch per second.

References Cited by the Examiner UNITED STATES PATENTS 1,920,075 7/1933Haenichen 10298 3,006,743 10/1961 Fox et al 149-22 3,028,432 4/1962 Ross14922 3,048,112 8/1962 Shope 102-98 3,052,092 9/1962 Kirkbride 10298 X3,073,242 1/1963 Hewson 10298 3,149,168 9/1964 Karlan et a1 149--22OTHER REFERENCES Solid Fuel Ind. Round-Up (referred to herein as SolidFuel), Missiles and Rocket Magazine, vol. 2, No. 8, August 1957, pp.6773 required.

Warren: Rocket Propellants, pp. 11, 23, 28-39 required (Reinhold Pub.Co., New York, N.Y., 1958).

BENJAMIN A. BORCHELT, Primary Examiner. SAMUEL FEINBERG, Examiner.

1. A GENERALLY CYLINDRICAL END BURNING PROPELLENT GRAIN HAVING A FLATCIRCULAR BASE AT ONE END AND A SEMISPHERICAL PORTION AT THE OTHER END,SAID PROPELLENT COMPRISING TWO CHARGES, ONE OF SAID CHARGES HAVING AFAST AND THE OTHER OF SAID CHARGES HAVING A SLOWER-BURNING RATE, A FIRSTCONICAL SLOWER-BURNING CHARGE POSITIONED ALONG THE LONGITUDINAL AXIS OFTHE CYLINDRICAL PROPELLENT GRAIN, THE APEX OF THE SAID CONICAL PORTIONBEING LOCATED IN THE PLANE OF SAID CIRCULAR BASE, THE BASE OF THECONICAL PORTION BEING INTEGRAL WITH THE SEMISPHERICAL PORTION, ANANNULAR FASTBURNING CHARGE SURROUNDING AND IN CONTACT WITH THE CONICALSLOWER-BURNING CHARGE, SAID FAST-BURNING CHARGE HAVING A BASE PORTIONLOCATED IN THE PLANE OF THE SAID CIRCULAR BASE; SAID ANNULARFAST-BURNING CHARGE HAVING WALLS NARROWLY TAPERING FROM SAID BASE ANDEXTENDING TO SAID SEMISPHERICAL PORTION, A SECOND-SLOWER BURNING ANNULARCHARGE SURROUNDING AND IN CONTACT WITH SAID FASTBURNING CHARGE, SAIDSECOND SLOWER-BURNING CHARGE HAVING A BASE PORTION LOCATED IN THE PLANEOF THE SAID CIRCULAR BASE AND HAVING A NARROWLY TAPERED WALL EXTENDINGTO SAID SEMISPHERICAL PORTION.